Leak stop plug against needle piercing and method of manufacturing the leak stop plug

ABSTRACT

A pierceable stopper enhanced in elasticity so that the liquid in a container will not leak even after a hollow needle inserted into the container through the pierceable stopper has been removed therefrom and a method of producing the pierceable stopper are provided. A pierceable part ( 11 ) through which a hollow needle is inserted into a container ( 2 ) is molded from a thermoplastic synthetic resin elastic material. The pierceable part is heat-treated with heated air at a temperature of from 80 to 120° C. to remove the internal stress. The heat-treated pierceable part ( 11 ) is inserted into an injection mold ( 20, 21 ). A molten thermoplastic synthetic resin is injected into a cavity ( 26 ) corresponding to a stopper body ( 10 ), which is defined by the injection mold ( 20, 21 ) and the pierceable part ( 11 ), to form a pierceable stopper ( 5 ).

TECHNICAL FIELD

[0001] The present invention relates to a pierceable stopper used for aliquid container into which a hollow needle can be externally insertedthrough the pierceable stopper, and also relates to a method ofproducing the pierceable stopper. More particularly, the presentinvention relates to a pierceable stopper for a medical liquid bottle,bag or the like filled with a liquid for medical treatment. Thepierceable stopper is made of a thermoplastic synthetic resin elasticmaterial and a thermoplastic synthetic resin material and has apierceable part enhanced in elasticity so that it is readily pierceablewith a hollow needle for injection or intravenous drip infusion, and yetthere is no leakage of medical liquid. The present invention alsorelates to a method of producing the above-described pierceable stopper.

BACKGROUND ART

[0002] Capsules filled with medical liquids for injection and bottles orbags filled with medical liquids for intravenous drip infusion arepreferably designed so that the medical liquids therein can be taken outor a liquid can be injected thereinto without removing the caps orstoppers therefrom. Therefore, the caps and stoppers are arranged sothat even when they are pierced with a hollow needle for injection orintravenous drip infusion and the needle is temporarily pulled out, theliquids in the containers cannot spill out, and, at the same time,foreign matter, e.g. air, in the hospital cannot enter the containers.Such stoppers are desirably mass-produced and reduced in cost so as tobe used by an increased number of people.

[0003] Conventionally, vulcanized rubber is used as a material for sucha stopper. However, the stopper using vulcanized rubber involves such adanger that an additive, a polymerization solvent, etc. in thevulcanized rubber may flow out into the medical liquid in the container,or rubber chippings cut by a hollow needle for injection or the like mayget mixed in the medical liquid. Accordingly, a stopper using athermoplastic synthetic resin elastic material (“elastic material” willhereinafter occasionally be referred to as “elastomer”) has beenproposed [Japanese Patent Application Unexamined Publication (KOKAI) No.Hei 9-173417].

[0004] The inventors of the present invention also proposed a techniquein Japanese Patent No. 3142521, Japanese Patent Application UnexaminedPublication (KOKAI) No. 2001-258991, etc., wherein the pierceable partof a pierceable stopper is made by using a thermoplastic synthetic resinelastic material lower in elasticity than rubber to prevent leakage ofliquid from the container after the removal of the inserted needle. Inthe conventional pierceable stoppers, however, the strain during moldingcarried out when they are produced remains in the pierceable parts asresidual stress, and this exceeds the elastic limit. Consequently,elastic recovery force becomes unfavorably weak. If a materialexhibiting high elasticity is used to solve this problem, the pierceablestopper becomes difficult to use because the pierceable part is hard andoffers a high resistance to a hollow needle when stuck thereinto.

[0005] There has also been proposed a stopper comprising two layers ofthermoplastic synthetic resin elastomers. However, satisfactory effectcannot be obtained with this stopper because there may be a littleleakage of medical liquid when the piercing conditions are severe. Thus,the user is not always satisfied with this stopper. Accordingly, therehas been a demand for a further improved pierceable stopper.

[0006] The present invention was made to solve the above-describedproblems and to improve the above-described technique disclosed inJapanese Patent No. 3142521 and Japanese Patent Application UnexaminedPublication (KOKAI) No. 2001-258991 by the inventors of the presentinvention, thus attaining the following objects.

[0007] An object of the present invention is to provide a pierceablestopper in which a pierceable part is previously heat-treated after ithas been molded, that is, the residual stress in the pierceable part isresolved previously, thereby enhancing elasticity. Thereafter, athermoplastic synthetic resin material is injection-molded, therebyallowing the pierceable part to recover by the elasticity after theremoval of the inserted needle, and thus preventing leakage of liquidfrom the container. Another object of the present invention is toprovide a method of producing the above-described pierceable stopper.

[0008] Still another object of the present invention is to provide apierceable stopper that can be produced at a reduced cost, and toprovide a method of producing the pierceable stopper.

[0009] The advantage of the pierceable stopper according to the presentinvention is as follows. In the pierceable stopper, the pierceable part,which is pierceable with a hollow needle, is formed by using athermoplastic synthetic resin elastic material treated to resolve theresidual stress (internal stress). Accordingly, there is no leakage ofliquid from the container when the pierceable part is pierced with ahollow needle or after the needle has been pulled out. Thus, there is nopossibility of the medical liquid splashing over the surroundings.

DISCLOSURE OF THE INVENTION

[0010] To attain the above-described objects, the present inventionprovides the following means: A pierceable stopper according to thepresent invention has a pierceable part pierceable with a hollow needle.The pierceable part is formed by using a thermoplastic synthetic resinelastic material as a base polymer. The thermoplastic synthetic resinelastic material is a styrene elastomer consisting essentially of ahydrogenated product of a styrene-conjugated diene block copolymerhaving a weight-average molecular weight not less than 150,000, whereinthe conjugated diene is at least one selected from isoprene andbutadiene. The pierceable part has a hardness in the range of from 20 to80 in terms of JIS(A) hardness and a thickness in the range of from 2millimeters to 8 millimeters.

[0011] The pierceable stopper further has a stopper body formed from athermoplastic synthetic resin having a higher rigidity than that of thematerial of the pierceable part. The stopper body has an outerperipheral portion for preventing a stress from propagating to theoutside when the pierceable part is pierced with the hollow needle andfor defining the pierceable part.

[0012] Further, the pierceable stopper has a thermowelded joint at whichthe pierceable part and the stopper body are thermowelded together.

[0013] The pierceable part, which has been molded, is heated to performa heat treatment for removing an internal stress. The heat-treatedpierceable part is inserted into an injection mold, and a melt of thethermoplastic synthetic resin is injected into a cavity defined by theinjection mold and the pierceable part at an injection pressure notlower than 59 MPa to mold the stopper body. Further, the pierceable partand the stopper body are thermowelded together in the injection mold toform the thermowelded joint.

[0014] [Thermoplastic Synthetic Resin Elastic Material for PierceablePart]

[0015] The thermoplastic synthetic resin elastic material used as a basepolymer to form the pierceable part is a styrene elastomer consistingessentially of a hydrogenated product of a styrene-conjugated dieneblock copolymer having a weight-average molecular weight of from 270,000to 400,000, wherein the conjugated diene is at least one selected fromisoprene and butadiene.

[0016] Judging from the viewpoint of moldability, external appearanceand so forth, however, the thermoplastic synthetic resin elasticmaterial is a styrene elastomer having a weight-average molecular weightof from 270,000 to 400,000. The molecular weight of this elastomer isconsiderably high in view of the fact that the molecular weight ofstyrene elastomers generally used for other use applications is of theorder of from 70,000 to 120,000.

[0017] Styrene polymers applicable to the present invention consistessentially of a hydrogenated product of a styrene-conjugated dieneblock copolymer, wherein the conjugated diene is a polymer blockcomprising either butadiene or isoprene alone or a mixture of isopreneand butadiene.

[0018] Specific examples of hydrogenated styrene-conjugated diene blockcopolymers usable in the present invention are hydrogenatedstyrene-butadiene-styrene (SEBS) block copolymers, hydrogenatedstyrene-isoprene-styrene (SEPS) block copolymers, and hydrogenatedstyrene-isoprene-butadiene-styrene (SEEPS) block copolymers. Thesepolymer blocks may be used alone or in the form of a mixture of two ormore of them. The use of a hydrogenated SEEPS block copolymer forforming the pierceable part in the present invention is particularlyeffective because the molecular weight of the base polymer can bedesigned to be large in comparison to hydrogenated SEBS and SEPS blockcopolymers.

[0019] When a mixture of isoprene and butadiene is used as theconjugated diene, the mixing weight ratio (isoprene/butadiene) is from(99/1) to (1/99), preferably from (90/10) to (65/35). It is important touse a hydrogenated styrene-conjugated diene block copolymer having astyrene content of from 5 to 50% by weight, preferably from 8 to 45% byweight, particularly preferably from 10 to 40% by weight, a 1,2-microstructure of less than 20%, preferably less than 15%, and ahydrogenation ratio of not less than 85%, preferably from 97 to 100%.

[0020] The weight-average molecular weight of a thermoplastic syntheticresin elastic material used in the present invention is measured by GPC(Gel Permeation Chromatography) and expressed in terms of polystyreneweight-average molecular weight as measured under the conditions shownbelow. Specific measuring conditions are as follows.

[0021] (Average Molecular Weight Measuring Conditions) Equipment: 150CALC/GPC (available from MILLIPORE, U.S.A.) Columns: ADM/S (availablefrom Showa Denko, Japan) 3 columns Solvent: o-dichlorobenZeneTemperature: 140° C. Flow velocity: 1 ml/min. Injected quantity: 200 μlConcentration: 2 mg/ml [antioxidant 2,6-di-t-butyl-p-phenol was added inan amount of 0.2% by weight. Concentration was measured at a wavelengthof 3.42 μm with an infrared spectrophotometer “MIRAN 1A” (trademark),available from FOXBORO (U.S.A.)]

[0022] It is desirable that the readily deflectable portion should beformed by deflecting the pierceable part in the direction of penetrationof the hollow needle during the process of molding the stopper body. Thehardness of the pierceable part should preferably be selected within therange of from 20 to 70 in terms of JIS(A) hardness (durometer hardness).It is preferable that the hardness of the pierceable part should bewithin the range of from 45 to 65 in terms of JIS(A) hardness of themeasured value obtained with a durometer of the type A defined by JISK6253.

[0023] It is particularly preferable that the pierceable part should beformed from a mixture of the above-described SEEPS block copolymer, aparaffin oil, and a polyolefin resin from the viewpoint of hardness,compatibility and so forth.

[0024] [Structure of Pierceable Part]

[0025] The pierceable part should preferably be formed from theabove-described styrene elastomer. It is preferable that the stopperbody should be formed from a thermoplastic synthetic resin andthermowelded to the pierceable part. The thermowelding process may beultrasonic welding whereby different kinds of plastic materials arewelded together by ultrasonic vibration. It is preferable that thestopper body should be welded to the pierceable part under pressure inan ultrasonic injection mold. The thickness of the readily deflectableportion is desirably in the range of from 1 to 10 millimeters, moredesirably in the range of from 2 to 5 millimeters. The hardness,thickness and other structural requirements demanded for the pierceablepart are substantially the same as in the publicly known techniquedisclosed in Japanese Patent No. 3142521.

[0026] [Heat Treatment]

[0027] The heat treatment applied to the pierceable part is a treatmentfor removing the internal stress. The heat treatment is characterized bybeing carried out for a period of time in the range of from 30 minutesto 12 hours by using heated air at a temperature of from 80 to 120° C.It is also possible to obtain favorable effects by carrying out the heattreatment at a temperature of 100 to 120° C. for 1 to 2 hours. The heattreatment may be performed in a heated liquid in place of heated air.

[0028] [Method of Producing Pierceable Stopper]

[0029] In addition, the present invention provides a method of producinga pierceable stopper having a pierceable part pierceable with a hollowneedle. The pierceable part is formed by using a thermoplastic syntheticresin elastic material as a base polymer. The thermoplastic syntheticresin elastic material is a styrene elastomer consisting essentially ofa hydrogenated product of a styrene-conjugated diene block copolymerhaving a weight-average molecular weight not less than 150,000, whereinthe conjugated diene is at least one selected from isoprene andbutadiene. The pierceable part has a hardness in the range of from 20 to80 in terms of JIS(A) hardness and a thickness in the range of from 2millimeters to 8 millimeters. The pierceable stopper further has astopper body formed from a thermoplastic synthetic resin having a higherrigidity than that of the material of the pierceable part. The stopperbody has an outer peripheral portion for preventing a stress frompropagating to the outside when the pierceable part is pierced with thehollow needle and for defining the pierceable part. Further, thepierceable stopper has a thermowelded joint at which the pierceable partand the stopper body are thermowelded together.

[0030] According to the pierceable stopper producing method, thepierceable part, which has been molded, is heat-treated. Theheat-treated pierceable part is inserted into an injection mold. A meltof the thermoplastic synthetic resin is injected into a cavity definedby the injection mold and the pierceable part at an injection pressurenot lower than 59 MPa to mold the stopper body, and the pierceable partand the stopper body are thermowelded together in the injection mold toform the thermowelded joint.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is a sectional view of the pierceable stopper according tothe present invention when it is applied to a medical liquid bag forintravenous drip infusion.

[0032]FIG. 2 is a flowchart showing the process of producing thepierceable stopper, in which the pierceable part is heat-treated.

[0033]FIG. 3 is a sectional view showing a mold for forming thepierceable stopper by injection molding process.

[0034]FIG. 4 is a sectional view showing a mold for forming thepierceable stopper by injection molding process according to anotherembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

[0035] Embodiments of the present invention will be described below withreference to the accompanying drawings. FIG. 1 shows an example in whichthe pierceable stopper according to the present invention is applied toa medical liquid bag for intravenous drip infusion. The structure andfunction of this application example are publicly known and detailed inJapanese Patent No. 3142521, Japanese Patent Application UnexaminedPublication (KOKAI) No. 2001-258991, and so forth. The applicationexample will be outlined below with a view to facilitating theunderstanding of the present invention. A medical liquid container 1 forintravenous drip infusion has a container body 2 made of a film-shapedtransparent synthetic resin material, e.g. polyethylene. The containerbody 2 contains a medical liquid.

[0036] The container body 2 has an opening 3 formed at the top thereof.One end of an annular connecting pipe is inserted into the opening 3.The opening 3 and the connecting pipe 4 are thermowelded together byultrasonic welding or the like. One end of a pierceable stopper 5 isinserted into and connected to the upper end of the connecting pipe 4.The connecting pipe 4 and the pierceable stopper 5 are also thermoweldedtogether by ultrasonic welding or other similar means.

[0037] The pierceable stopper 5 comprises a stopper body 10, apierceable part 11, an external hermetic sealing film 12, and aninternal hermetic sealing film 13. The external hermetic sealing film 12is a kind of partition for preventing the pierceable part 11 and theoutside air from coming into direct contact with each other. Theinternal hermetic sealing film 13 is a partitioning member provided toprevent the pierceable stopper 5 and the medical liquid in the containerbody 2 from coming into direct contact with each other and to maintainthe airtightness of the container body 2. The internal hermetic sealingfilm 13 and the container body 2 are joined together by using a publiclyknown technique, e.g. thermowelding using ultrasonic waves or bondingusing an adhesive.

[0038] The pierceable part 11 and the stopper body 10, which constitutethe pierceable stopper 5, are formed by using different kinds ofsynthetic resin materials. The pierceable part 11 is disposed inside thestopper body 10 and secured thereto. The pierceable part 11 ispositioned in the central portion of the stopper body 10. The stopperbody 10 and the pierceable part 11 are integrally molded by an insertdissimilar material injection molding process (described later). Thestopper body 10 is made of a thermoplastic synthetic resin havingmechanical strength, e.g. polypropylene (PP), polyethylene (PE), ABSresin (ABS), polycarbonate (PC), or polyamide (PA).

[0039] It should be noted that a styrene elastomer is preferably used asa material for the pierceable part 11 as described later, andpolypropylene (PP), polyethylene (PE) or ABS resin (ABS) is preferablyused as a material for the stopper body 10 to allow the stopper body 10to be thermowelded to the material of the pierceable part 11. As amaterial for the pierceable part 11, various thermoplastic syntheticresin elastic materials can be used. Thermoplastic synthetic resinelastic materials usable in the present invention include nylon,polyurethane, olefin, polyester and styrene elastomers having a JIS(A)hardness of 20 to 65 degrees, which is lower than the hardness ofthermoplastic synthetic resins. One or more thermoplastic syntheticresin elastic materials are optionally selected from those mentionedabove and used alone or in the form of a mixed elastomer.

[0040] If the JIS(A) hardness is less than 20, the material strength isweak, so that the pierceable part 11 is likely to tear when a hollowneedle is inserted thereinto. If JIS(A) hardness of the measured valueobtained with a durometer of the type A defined by JIS K6253 is morethan 65 degrees, the material is excessively hard and offers a highresistance to penetration of the needle. Accordingly, operability ispoor.

[0041] Among the thermoplastic synthetic resin elastic materials,styrene elastomers are particularly preferable. Typical styreneelastomers are hydrogenated products of SEBS(styrene-ethylene-butylene-styrene), SEPS(styrene-ethylene-propylene-styrene) and SEEPS(styrene-isoprene-butadiene-styrene) block copolymers. At least one ofthese styrene elastomers is used in this embodiment. Among theabove-mentioned styrene elastomers, SEEPS highly-saturated hydrogenatedstyrene elastomers are preferable.

[0042] When a styrene elastomer is applied to the present invention, itis generally used in the form of a compound containing one or more ofthe above-mentioned SEBS, SEPS and SEEPS hydrogenated styrene elastomersas a base polymer. Raw materials to be compounded are mixed togetherroughly in the following compounding ratio:

SEBS, SEPS, SEEPS or a mixture thereof . . . 100 parts by weight   (1)

Paraffin oil . . . 50 to 300 parts by weight   (20)

Polyolefin resin . . . 10 to 50 parts by weight   (3)

[0043] It should be noted that 50 to 40 parts by weight of an inorganicfiller may be added to the materials (1) to (3) according to need.Styrene elastomers applicable to the present invention, i.e. (1) SEPS,SEBS, or a mixture thereof, are commercially available in the name of“Septon” (trademark) available from Kuraray Co., Ltd. (Japan), “CleitonG (trademark) available from Cleiton Polymer Japan (Japan), and“Rabalon” (trademark) available from Mitsubishi Petro-Chemical Co., Ltd.(Japan). It is necessary to select a base polymer having a specificmolecular weight from among these styrene elastomers. Paraffin oilusable as the above (2) is as follows.

[0044] Oils having a kinematic viscosity of 200 to 800 centistokes(cSt), preferably 500 to 600 cSt, at 40° C., and an ignition point (COC)of 200 to 400° C., preferably 250 to 350° C., are suitably used. Oilsare, in general, mixtures of three, i.e. aromatic ring, naphthene ring,and paraffin chain, and classified as follows. An oil in which thenumber of carbon atoms present in the paraffin chains accounts for notless than 50% by weight of the total number of carbon atoms is referred.An oil in which the number of carbon atoms accounts for 30 to 45% byweight of the total number of carbon atoms is referred to as “naphtheneoil”. An oil in which the number of carbon atoms present in the aromaticrings accounts for not less than 30% by weight of the total number ofcarbon atoms is referred to as “aromatic oil”.

[0045] If the pierceable part 11 is pierced with a hollow needle, therewill be no leakage from a crack, tear or cut opening which may be madein a pierced portion thereof. When the pierceable part 11 is piercedwith a hollow needle, a tear or an opening is formed therein by thewedge action of the needle. After the formation of the tear or openingin the pierceable part 11, the medical liquid in the container body 2needs to be prevented from leaking out through the tear or the openingin a state where the needle is stuck into the pierceable part 11 or hasbeen pulled out from it. The main reason for the leakage is presumed asfollows. Penetration of the needle into the pierceable part 11 causespermanent set, more precisely, permanent compression set, to be formedaround the opening made by the insertion of the needle. Consequently,the pierceable part 11 cannot elastically recover from the deformation,or even if it recovers, the pierceable part 11 cannot be ensured asufficient elastic recovery force to close the opening.

[0046] That is, if the pierceable part 11 is ensured a sufficientelastic recovery force to close the tear or the opening, the leakage canbe prevented. In the present invention, the problem of leakage is solvedby subjecting the pierceable part 11 to a heat treatment, that is, atreatment for removing the internal stress. The internal stressdisorders the dimensional accuracy of the product and also causesshrinkage, deformation and breakage. In particular, the internal stressunfavorably limits the elasticity required for the use application ofthe present invention.

[0047] The pierceable part 11 is molded from a thermoplastic syntheticresin elastic material filled in an injection mold. Because thethermoplastic synthetic resin elastic material is a material havingrubber-like elasticity and forcedly filled into the injection mold, thepierceable part 11 has an orientation strain produced in the directionof flow of the material. The strain cannot be removed simply by removingthe applied pressure. More specifically, because it is immediatelycooled to solidify in the injection mold, the material cannot return toits original shape. Hence, the orientation strain remains in the form ofresidual stress (internal stress). According to the present invention,as shown in FIG. 2, step B of heat-treating the pierceable part 11 isadded after step A of molding the pierceable part 11. That is, a heattreatment (annealing) is performed after the molding process to removethe residual stress.

[0048] The heat treatment exhibits the effect of preventing the leakageof liquid. More specifically, because the pierceable part 11 is heatedagain, the internal stress is resolved, and the orientation strain isrelaxed. Consequently, the balance between the direction of flow of thematerial from the gate and the direction perpendicular to the materialflow direction is bettered. Thus, the leakage of liquid is preventedeffectively. That is, the ratio of MD (Machine Direction) to TD(Transverse direction) becomes close to 1. In the heat treatment, thepierceable part 11 is heated in an atmosphere of heated air at atemperature roughly in the range of from 80 to 120° C. for a period oftime in the range of from 30 minutes to 12 hours, although theheat-treating conditions depend on the kind of resin used. The heattreatment can be performed with a simple, common device, e.g. an oven.

[0049] Accordingly, the residual stress can be removed at a reduced costwithout requiring costly equipment. By removing the strain, theelasticity of the material constituting the pierceable part 11 isrecovered. As a result, the elastic recovery force of the pierceablepart 11 is increased. Consequently, when the pierceable part 11 ispierced with a hollow needle or after the needle has been pulled outfrom it, the tear or cut opening made in the pierced portion thereof isclosed by the enhanced elasticity of the material. Accordingly, therewill be no leakage of medical liquid from the tear or the opening. Inactual practice, a favorable result can be obtained by performing theheat treatment at a temperature in the range of from 100 to 120° C. fora period of time in the range of from 1 to 2 hours. Subsequently, thepierceable part 11, which has been subjected to the removal of strain,is inserted into a mold for injection molding (C in FIG. 2).

[0050] After the pierceable part 11 has been placed in a predeterminedposition, a thermoplastic synthetic resin is injected into the mold toform a stopper body 10 (D in FIG. 2). Thus, a pierceable stopper 5 isformed (E in FIG. 2). A specific molding process of this process will beshown below with reference to FIG. 3. It should be noted that a forcedmoisture absorption treatment (moisture conditioning treatment) shoulddesirably be carried out in combination with the heat treatmentaccording to the kind of resin used. The forced moisture absorptiontreatment allows the dimensional stability and toughness to bemaintained.

[0051]FIG. 3 shows a section of a mold assembly for injection mold. Theheat-treated pierceable part 11 is inserted into the mold assembly forinjection molding. The mold assembly is adapted to mold a stopper body10 by injection molding to form a pierceable stopper 5. The moldassembly is formed from a stationary mold element 20 and a movable moldelement 21. The stationary mold element 20 is provided with a gate 22and a runner 23 communicating with the gate 22. When the stationary moldelement 20 and the movable mold element 21 are in a closed position, afirst cavity 25 is defined therebetween. The pierceable part 11, whichhas previously been molded and subjected to strain removal, is insertedinto the first cavity 25.

[0052] Accordingly, a second cavity 26 is defined between the stationarymold element 20, the movable mold element 21 and the pierceable part 11.The second cavity 26 is a cylindrical space for forming the stopper body10. A molten thermoplastic synthetic resin for forming the stopper body10 is injected into the second cavity 26, thereby forming the stopperbody 10. The molten thermoplastic synthetic resin forms the stopper body10 while applying pressure to the pierceable part 11 from the outerperiphery thereof. In other words, the pierceable stopper 5 is formed ina state where the pierceable part 11 is compressed.

[0053] As the injection pressure for the thermoplastic synthetic resin,such a pressure is applied as causes a larger amount of volume reductionthan the amount of volume reduction caused by the natural shrinkage of amelt, a semi-melt or a solid due to a temperature drop. Morespecifically, the resin melt is injected at a pressure higher than thenormal injection pressure regarded as the optimum injection conditionfor the thermoplastic synthetic resin. When the viscosity of thethermoplastic synthetic resin is high, the injection molding pressure isset at a slightly higher level. It is desirable that the thermoplasticsynthetic resin melt should be injected at an injection pressure notlower than 59 MPa to form the stopper body 10.

[0054] Meanwhile, the stopper body 10 and the pierceable part 11 arethermowelded together in the injection mold by melting the surface ofthe thermoplastic synthetic resin elastic material of the pierceablepart 11 with the heat of the molten thermoplastic synthetic resin forforming the stopper body 10. When the pierceable part 11 is pierced witha hollow needle, even if the pierced portion is cut open, the opening isclosed by the elasticity recovered by the strain removal and an elasticrecovery force derived from the compressive internal stress. Therefore,there is no possibility of leakage of the medical liquid from thecontainer. In addition, the thermowelded joint prevents the leakage ofliquid even more effectively.

[0055] (Other Embodiments)

[0056]FIG. 4 is a sectional view showing a production process in a casewhere the pierceable part is different in shape from the above. In thisexample, a pierceable part 30 has a recessed portion 31. The pierceablepart 30 is pressurized in such a manner as to be clamped at the outerperiphery thereof by the pressure applied by the injected molten resinfor forming a stopper body 39. Thus, the pierceable part 30 iscompressed by the injection pressure. The mold structure will bedescribed below. A previously molded pierceable part 30 has beeninserted into a first cavity 32. A cylindrical slide core 33 has beeninserted into the recessed portion 31 of the pierceable part 30.

[0057] The slide core 33 is movable into the recessed portion 31. Theamount to which the slide core 33 projects into the recessed portion 31is adjustable. A second cavity 36 is defined between a stationary moldelement 34, a movable mold element 35 and the pierceable part 30 to forma space for forming the stopper body 39 in the same way as the above. Inaddition, a gap S is formed between the slide core 33 and the recessedportion 31 of the pierceable part 30 placed in the first cavity 32. Amolten thermoplastic synthetic resin is injected into the second cavity36 of the above-described mold structure through a runner 37 and a gate38 under the same conditions as the above.

[0058] The pierceable part 30 is deformed by the compressive pressure ofthe injected resin to fill the gap S provided in the recessed portion 31of the pierceable part 30. Therefore, when the pierceable stopper isremoved from the mold after the injection molding process, thepierceable part 30 is elastically deformed, although the deformation isonly slight. The recessed portion of the pierceable part 30 formslocally a readily deformable portion. Accordingly, when the pierceablepart 30 is pierced with a hollow needle for intravenous drip infusion,the recessed portion 31 is deformed so as to surround the needle and tocome in surface contact with the outer surface of the needle.Accordingly, the liquid is unlikely to leak. The pierceable part 30having the recessed portion 31 should also be heated-treated before thestopper body 39 is formed by injection molding. By doing so, theabove-described leak preventing effect is further enhanced.

[0059] It should be noted that containers to which the present inventionis applicable are not limited to those of the type adapted to take out aliquid therefrom. The present invention is also applicable to containersof the type that a liquid is externally injected thereinto through ahollow needle.

EXPERIMENTAL EXAMPLES

[0060] An experiment was carried out under the following conditions toconfirm the performance of the pierceable stopper 5 produced accordingto the above-described first embodiment. The pierceable part 11 wasformed by using a styrene elastomer as a base polymer, i.e. “Septon 4077” (trademark), available from Kuraray Co., Ltd. (consisting essentiallyof SEEPS and having a molecular weight of 300,000). The styreneelastomer was used in the form of a compound formed by kneading Septon4077, a paraffin oil and polypropylene in the mixing ratio of 40:50:10with a twin-screw extruder. The hardness of the pierceable part was 49in terms of JIS(A) hardness.

[0061] The stopper body 10 was molded under the following moldingconditions by using polypropylene (BC03C, available from Nippon PolychemCorp.) as a thermoplastic synthetic resin.

[0062] The injection molding conditions for the stopper body 10 were asfollows. The injection temperature was 210° C., and the injectionpressure was 78 MPa (800 kgf/cm²). The injection molding conditions forthe pierceable part 11 were as follows. The injection temperature was200° C., and the injection pressure was 49 MPa (500 kgf/cm²). The wallthickness of the pierceable part 11 was 4.8 millimeters. Theheat-treating conditions were as follows. The resin temperature was 115°C., and the heating time was 1 hour or 8 hours.

[0063] Table 1 below shows the results of a liquid leakage test. In thetest, each pierceable stopper was pierced with a plastic needle forintravenous drip infusion having a diameter of 4 millimeters, and leftto stand for 1 hour or 5 hours under ordinary temperature conditions.Then, the condition of leakage after the removal of the needle wasvisually judged. The test was carried out 5 times for each of the testconditions concerning the period of time of piercing with the needle,i.e. 1 hour, and 5 hours. TABLE 1 Results of Liquid Leakage Test Periodof time of piercing with Heat-treating Test results needle conditions (N= 5) 1 hour  Not heat-treated Δ, Δ, Δ, Δ, Δ 115° C., 1 hour ⊚, Δ, ⊚, ⊚,⊚ 115° C., 8 hours ⊚, ⊚, ⊚, ⊚, ⊚ 5 hours Not heat-treated Δ, Δ, Δ, X, Δ115° C., 1 hour ⊚, Δ, Δ, ⊚, ⊚ 115° C., 8 hours ⊚, ⊚, ⊚, ⊚, ⊚

[0064] Table 2 below shows the results of the test carried out onpierceable stoppers produced under injection pressure and heat-treatingconditions different from those for the pierceable stoppers in Table 1under the same testing conditions as in the case of Table 1. TABLE 2Results of Liquid Leakage Test Period of time of Heat- piercing treatingInjection pressure Test results with needle conditions for stopper body(n = 5) 1 hour 115° C.  39 MPa (Comp. Ex.) X, X, Δ, Δ, Δ 3 hours  59 MPa(Example) Δ, ⊚, ⊚, ⊚, ⊚ 108 MPa (Example) ⊚, ⊚, ⊚, ⊚, ⊚

What is claimed is:
 1. A pierceable stopper comprising: a pierceablepart pierceable with a hollow needle, said pierceable part being formedby using a thermoplastic synthetic resin elastic material as a basepolymer, said thermoplastic synthetic resin elastic material being astyrene elastomer consisting essentially of a hydrogenated product of astyrene-conjugated diene block copolymer having a weight-averagemolecular weight not less than 150,000, wherein said conjugated diene isat least one selected from isoprene and butadiene, said pierceable parthaving a hardness in a range of from 20 to 80 in terms of JIS(A)hardness and a thickness in a range of from 2 millimeters to 8millimeters; a stopper body formed from a thermoplastic synthetic resinhaving a higher rigidity than that of the material of said pierceablepart, said stopper body having an outer peripheral portion forpreventing a stress from propagating to an outside when said pierceablepart is pierced with said hollow needle and for defining said pierceablepart; and a thermowelded joint at which said pierceable part and saidstopper body are thermowelded together; wherein said pierceable part,which has been molded, is heated to perform a heat treatment forremoving an internal stress and then inserted into an injection mold,and a melt of the thermoplastic synthetic resin is injected into acavity defined by said injection mold and said pierceable part at aninjection pressure not lower than 59 MPa to mold said stopper body, andfurther, said pierceable part and said stopper body are thermoweldedtogether in said injection mold to form the thermowelded joint.
 2. Apierceable stopper according to claim 1, wherein said heat treatment iscarried out for a period of time in a range of from 30 minutes to 12hours by using heated air at a temperature of from 80 to 120° C.
 3. Apierceable stopper according to claim 1 or 2, wherein said thermoplasticsynthetic resin elastic material is a styrene elastomer consistingessentially of a hydrogenated product of a styrene-conjugated dieneblock copolymer having a weight-average molecular weight of from 270,000to 400,000, wherein said conjugated diene is at least one selected fromisoprene and butadiene.
 4. A pierceable stopper according to claim 1 or2, wherein said thermoplastic synthetic resin elastic material is ahydrogenated product of a styrene-isoprene-butadiene-styrene blockcopolymer having a weight-average molecular weight of from 270,000 to400,000.
 5. A pierceable stopper according to claim 4, wherein saidpierceable part is formed from a mixture of said hydrogenated product ofa styrene-isoprene-butadiene-styrene block copolymer, a paraffin oil,and a polyolefin resin.
 6. A pierceable stopper according to claim 4,wherein said thermoplastic synthetic resin is at least one selected frompolypropylenes, polyethylenes, and ABS resins.
 7. A method of producinga pierceable stopper, said pierceable stopper having: a pierceable partpierceable with a hollow needle, said pierceable part being formed byusing a thermoplastic synthetic resin elastic material as a basepolymer, said thermoplastic synthetic resin elastic material being astyrene elastomer consisting essentially of a hydrogenated product of astyrene-conjugated diene block copolymer having a weight-averagemolecular weight not less than 150,000, wherein said conjugated diene isat least one selected from isoprene and butadiene, said pierceable parthaving a hardness in a range of from 20 to 80 in terms of JIS(A)hardness and a thickness in a range of from 2 millimeters to 8millimeters; a stopper body formed from a thermoplastic synthetic resinhaving a higher rigidity than that of the material of said pierceablepart, said stopper body having an outer peripheral portion forpreventing a stress from propagating to an outside when said pierceablepart is pierced with said hollow needle and for defining said pierceablepart; and a thermowelded joint at which said pierceable part and saidstopper body are thermowelded together; said method comprising the stepsof heating said pierceable part, which has been molded, to perform aheat treatment for removing an internal stress; inserting saidpierceable part, which has been heat-treated, into an injection mold;injecting a melt of the thermoplastic synthetic resin into a cavitydefined by said injection mold and said pierceable part at an injectionpressure not lower than 59 MPa to mold said stopper body; andthermowelding together said pierceable part and said stopper body insaid injection mold to form the thermowelded joint.
 8. A method ofproducing a pierceable stopper according to claim 7, wherein said heattreatment is carried out at a temperature of from 80 to 120° C. for aperiod of time in a range of from 30 minutes to 12 hours.
 9. A method ofproducing a pierceable stopper according to claim 7 or 8, wherein saidthermoplastic synthetic resin elastic material for forming saidpierceable part is a styrene elastomer consisting essentially of ahydrogenated product of a styrene-conjugated diene block copolymerhaving a weight-average molecular weight of from 270,000 to 400,000,wherein said conjugated diene is at least one selected from isoprene andbutadiene.
 10. A method of producing a pierceable stopper according toclaim 7 or 8, wherein said thermoplastic synthetic resin elasticmaterial for forming said pierceable part is a styrene elastomerconsisting essentially of a hydrogenated product of astyrene-isoprene-butadiene-styrene block copolymer having aweight-average molecular weight of from 270,000 to 400,000.
 11. A methodof producing a pierceable stopper according to claim 10, wherein saidthermoplastic synthetic resin for forming said stopper body is at leastone selected from polypropylenes, polyethylenes, and ABS resins.
 12. Apierceable stopper according to claim 10, wherein said pierceable partis formed from a mixture of said hydrogenated product of astyrene-isoprene-butadiene-styrene block copolymer, a paraffin oil, anda polyolefin resin.